1. Field of the Invention
The present invention relates to a method of successively forming and/or erasing images selectively in different portions of a recording layer of a recording medium which comprises a reversible thermosensitive recording material capable of repeatedly recording images therein and erasing the same therefrom.
2. Discussion of Background
Recently attention has been paid to a reversible thermosensitive recording material capable of temporarily recording images thereon and erasing the same therefrom when such images become unnecessary, and repeatedly performing such image recording and erasing operations.
For example, as disclosed in Japanese Laid-Open Patent Application 55-154198, there is conventionally known a reversible thermosensitive recording material in which an organic low-molecular-weight material such as a higher fatty acid is dispersed in a matrix resin such as a vinyl chloride based resin.
However, when images are formed in the conventional reversible thermosensitive recording material and erased therefrom many times by the application of heat thereto, especially using a thermal head, the surface of the reversible thermosensitive recording material takes scratches because both heat and pressure are applied to the recording material at the same time. As the scratches are increased on the surface of the recording material, it becomes difficult to carry out the image formation uniformly.
To reduce the scratches on the recording material when the thermal head is employed for image formation and erasure, the inventors of the present invention have proposed to provide a protective layer on the surface of the recording material, as disclosed in Japanese Laid-Open Patent Applications 63-221087, 63-317385 and 2-566. However, in the case where the image forming and erasing operation is repeated many times in the recording material, the surface of the recording material cannot be sufficiently protected from the scratches merely by forming the protective layer on the conventional reversible thermosensitive recording material.
In addition, when both heat and pressure are simultaneously applied to the recording material every time the image formation and erasure are performed, for instance, by using the thermal head, domains of the organic low-molecular-weight material, which is dispersed in the matrix resin at the initial stage, are apt to coalesce. As a result, the whiteness degree of a milky opaque portion in the recording material is decreased, and the image contrast is lowered.